ABSTRACT
The exploitation of user cooperation has been recognized as an important technique to improve the robustness of secure transmissions, where various studies have shown that a careful use of relaying can improve the receptional reliability of the legitimate receivers and decrease eavesdropping capabilities at the same time. In this chapter, a detailed review will be provided to illustrate how to integrate relay transmissions with secrecy communications. Simpler scenarios with single-antenna nodes will be investigated first, where two secure transmission strategies, cooperative jamming and relay chatting, will be focused particularly. Then scenarios with multiple-antenna nodes will be considered, and the design of precoding becomes of interest, where the cases with and without channel information at the transmitters will be discussed separately.
